1. Field of the Invention
The present invention relates to a cassette loading device for a recording and/or reproducing apparatus, and particularly to a cassette loading device in which magnetic tape cassettes of different sizes and weights can be smoothly and precisely loaded to the respective loading positions by a driving force suitable for their respective weights. Specifically, the present invention relates to a cassette loading device including a cassette holder which is capable of moving between a cassette insertion position and a cassette loading completed position.
2. Description of the Prior Disclosure
Recently, various cassette loading devices for magnetic tape cassettes applicable in recording and/or reproducing apparatus have been proposed and developed. For example, digital video tape recorders used at broadcasting stations are constructed so as to accept different sizes of tape cassettes having various maximum recording times. These tape cassettes contain magnetic tape 19 mm in width, 16 micron in thickness, 190 m (S size), 587 m (M size), or 1311 m (L size) in length. The respective sizes of tape cassettes have 11 min, 34 min, and 76 min rec/play times. The size of each magnetic tape cassette casing is defined in accordance with the length of the magnetic tape. The S size magnetic tape cassettes are 172 mm in length and 109 mm in width. The M size magnetic tape cassettes are 254 mm in length and 150 mm in width. The L size magnetic tape cassettes are 66 mm in length and 206 mm in width. The above prior art cassette loading apparatus can load different sizes of tape cassettes to the predetermined loading completed position. One such cassette loading apparatus has been disclosed in the U.S. Pat. No. 4,631,607.
Alternatively, cassette loading apparatus, which are capable of moving a reel driving device so as to match the interval, between the pair of reels in the cassette, by detecting the size of the tape cassette have been disclosed in U.S. Pat. Nos. 4,664,337 and 4,787,572.
Such prior art cassette loading apparatus are driven at a constant torque by a driving motor regardless of the size of the tape cassette. The weight of L size tape cassettes is substantially 1 kg greater than the weight of S size tape cassettes. Therefore, the driving torque suitable for loading the L size tape cassettes is larger than the driving torque suitable for the S size tape cassettes. Due to this excessive torque, the S size tape cassettes are driven too forcibly into the recording and/or reproducing apparatus, which tends to result in damage to the driving system.
Conversely, when the L size tape cassettes are inserted into the recording and/or reproducing apparatus with the driving torque suitable for the S size tape cassettes, the loading speed is slow. Moreover, insufficient driving torque results in deterioration in the positioning accuracy of the cassette loading device. As a result, the tape cassette is not precisely positioned in the loading completed position. If the magnetic tape is extracted from the tape cassette casing, while the cassette is improperly aligned, damage to the magnetic tape occurs.
If the driving torque is set to the value appropriate for the M size tape cassettes, the torque is greater than the optimum torque for the S size tape cassettes and less than the optimum torque for the L size tape cassettes. In this case, the loading apparatus cannot operate satisfactorily in loading the L and S size cassettes.